1. Field of the Invention
This invention relates to a method for improving fatigue strength due to repeated pressure at a branch hole part of a member for a high pressure fluid such as fuel injection system parts for forming a fuel injection system for a Diesel engine, for example, a fuel injection pump, a fuel injection nozzle, a fuel injection pipe, and a common rail, an injection pump, an injection nozzle, an injection pipe and a feedback pie for a fuel pressure accumulation system, a pressure vessel and the like, and a branch hole part of a member for a high pressure fluid formed by the method, and further to a member for a high pressure fluid with a built-in slider, thereby improving fatigue strength due to the repeated pressure at the branch hole part of a member for a high pressure fluid such as fuel injection system parts for forming a fuel injection system for a Diesel engine, for example, a fuel injection pump and a fuel injection nozzle, and an injection pump, an injection nozzle and so on for a fuel pressure accumulation system.
2. Description of the Prior Art
Conventionally, a branch hole part formed by a branch hole formed in the thickness part of a member for a high pressure fluid for communicating a hollow part of a member for a high pressure fluid of this type, or a flow passage of a member for a high pressure fluid with a built-in slider with a passage of a branch hole member is so constructed that a branch hole is bored in a hollow part or a flow passage (hereinafter referred to as a hollow part) formed by the inner peripheral surface having a circular section to be communicated with a passage of the branch hole member.
However, in such a structure that a branch hole is simply bored in the hollow part having a complete round section of a member for a high pressure fluid having a complete round section to be communicated with a passage of a branch hole member, when high repeated internal pressure is applied to the hollow part of the member for a high pressure fluid, the largest tensile stress is generated at the opening end part of an outlet of the branch hole in the hollow part of the member for a high pressure fluid, so that cracks due to metal fatigue caused by repeated pressure occur easily, with the opening end part as the starting point, resulting in the possibility of causing the leakage of a fluid.
As a measure to improve the fatigue strength due to such repeated pressure, an annular groove is formed on the inner peripheral surface of the hollow part including the outlet position of the branch hole, or a pocket is formed on the outlet of the branch hole on trial, but in the former case, it is necessary to adopt machining for accurately executing formation of an annular groove including the outlet of the branch hole, so the work requires much time to be quite unsuitable for the recent mass production system, and there is the possibility of damaging not only portions required to be machined by the other inner peripheral surfaces. On the other hand, in the latter case, as the formation of the above pocket is executed electrochemically, it agrees with the above mass production system, but actually stress is concentrated on the opening end part of the outlet of the branch hole in the hollow part of the member for a high pressure fluid, so that even if such a process is executed, it does not give much effect of improving fatigue strength.
This invention has been proposed in order to solve the described problems in the conventional branch hole part of a member for a high pressure fluid, and it is an object of the invention to provide a method for improving the fatigue strength due to repeated pressure at the branch hole part in a member for a high pressure fluid, by which the maximum stress value generated in an opening end part of an outlet of a branch hole on the hollow part side of the member for a high pressure fluid is lowered to further improve the internal pressure fatigue strength, a branch hole part of a member for a high pressure fluid formed by the method, and a member for a high pressure fluid with a built-in slider having the branch hole.
In order to accomplish the foregoing object, in accordance with a first embodiment of the present invention, there is provided a method for improving the fatigue strength due to repeated pressure at a branch hole part in a member for a high pressure fluid, characterized in that at the time of forming a branch hole communicated with a hollow part in a member for a high pressure fluid having the hollow part, the member for a high pressure fluid is pressed inward from the outside to form a part where compressive stress remains on the hollow part side inner peripheral surface and subsequently a branch hole opened to the hollow part is bored in the part to make the compressive residual stress exist at least in the peripheral edge of the branch hole.
In accordance with a second embodiment of the present invention, there is provided a method for improving the fatigue strength due to repeated pressure at a branch hole part in a member for a high pressure fluid, characterized in that at the time of forming a branch hole communicated with a hollow part in a member for a high pressure fluid having the hollow part, a branch hole opened to the inner peripheral surface of the member is bored in the member for a high pressure fluid and subsequently the branch hole part of the member for a high pressure fluid is pressed inward to the outside to make compression stress remain at least on a part of the peripheral edge of the branch hole in the hollow part side inner peripheral surface.
Further in accordance with a third embodiment of the present invention, there is provided a method for improving the fatigue strength due to repeated pressure at a branch hole part in a member for a high pressure fluid, characterized in that the time of forming a branch hole communicated with a hollow part in a member for a high pressure fluid having the hollow part, the member for a high pressure fluid is pressed inward from the outside to form a part where compressive stress remains on the hollow part side inner peripheral surface and simultaneously punch a branch hole opened to the hollow part, thereby making the compressive residual stress exist on the peripheral edge of the branch hole.
In accordance with a fourth embodiment of the present invention, there is provided a method for improving the fatigue strength due to repeated pressure at a branch hole part in a member for a high pressure fluid, characterized in that the time of forming a branch hole communicated with a hollow part in a member for a high pressure fluid having the hollow part, the member for a high pressure fluid is pressed inward from the outside a little eccentrically from a portion where to provide the branch hole to make compressive residual stress exist on the peripheral edge part of the branch hole.
Further in accordance with a fifth embodiment of the present invention, there is provided a method for improving the fatigue strength due to repeated pressure at a branch hole part in a member for a high pressure fluid, characterized in that the time of forming a branch hole communicated with a hollow part in a member for a high pressure fluid having the hollow part, the member for a high pressure fluid is pressed inward from the outside at least at two portions in the diametral direction a little eccentrically from a portion where to provide the branch hole.
Further in accordance with a sixth embodiment of the present invention, there is provided a method for improving the fatigue strength due to repeated pressure at a branch hole part in a member for a high pressure fluid, characterized in that at the time of forming a branch hole communicated with a hollow part in a member for a high pressure fluid having the hollow part, the member for a high pressure fluid is pressed inward from the outside to form a portion where compressive stress remains in a range wider than the area where to provide the branch hole in the hollow part side inner peripheral surface and bore a branch hole in the central part of the portion.
Further in accordance with a seventh embodiment of the present invention, there is provided a branch hole part of a member for a high pressure fluid, characterized in that a branch hole communicated with a hollow part is bored in the member for a high pressure fluid having the hollow part and the inner peripheral edge part of the branch hole has the compressive residual stress.
Further in accordance with an eighth embodiment of the present invention, there is provided a member for a high pressure fluid with a built-in slider having a branch hole, in a member for a high pressure fluid, which includes a hollow part in the axial interior and a branch hole communicated with the hollow part on at least one boss part provided on the axial peripheral wall part, and has a slider in the hollow part, wherein the pressing force is applied in the axial direction of the boss part by an external pressure system in such a manner that at least a part of the opening end part of the flow passage of the branch hole is projected, and then the projected part is removed to form a complete round inner peripheral surface.
Further in accordance with a ninth embodiment of the present invention, there is provided a member for a high pressure fluid with a built-in slide having a branch hole, in a member for a high pressure fluid which includes a hollow part in the axial interior and a branch hole communicated with the hollow part at least on one sleeve nipple part fitted the axial peripheral part by welding or brazing, and has a slider in the hollow part, wherein the pressing force is applied in the axial direction of the sleeve nipple by an external pressure system in such a manner that at least a part of the opening end part of a flow passage of the branch hole is projected, and then the projected part is removed to form a complete round inner peripheral surface.
That is, the present invention adopts the methods shown in the described first to sixth embodiments as a method for generating compressive residual stress in the periphery of the opening end part of an outlet of a branch hole in a hollow part of a member for a high pressure fluid, in which the compressive residual stress is made exist in the periphery of an opening end part of an outlet of a branch hole communicated with a passage of a branch hole member in a hollow part of a member for a high pressure fluid, whereby a high internal pressure of the hollow part of the member for a high pressure fluid, and if circumstances require, also the stress generated in the inner peripheral edge part of the lower end of the branch hole by the radial force applied to the wall thickness part of the member for a high pressure fluid at the time of putting the branch hole member in the connecting state are canceled by the compressive residual stress to lower the maximum tensile stress value generated in the inner peripheral edge part of the lower end of the branch hole.
Further, not to be a hindrance to sliding of a slider built in the hollow part, when the pressing force is applied to the member for a high pressure fluid from the outside so that the hollow part side inner peripheral surface is deformed and projected, the projected part is removed by cutting or grinding to form a complete round inner peripheral surface.
In this case, as a method for applying the pressing force to the member for a high pressure fluid from the outside, for example, used is a method in which with a member for a high pressure fluid fixed to a lower die, pressure is applied inward in the radial direction from the outside of the member for a high pressure fluid by a punch or a rod.
As described above, according to the present invention, the compressive residual stress is made exist in the periphery of an opening end part of a branch hole in the hollow part side branch hole part of the member for a high pressure fluid, whereby the generation of tensile stress in the inner peripheral edge of the lower end of the branch hole can be canceled by the compressive residual stress to be effectively restrained, so that it is possible to improved the internal pressure fatigue strength in the branch hole part of the member for a high pressure fluid.